There is a simple, elemental reason why "Diary of a Wimpy Kid: Dog Days" can be expected to strike a chord with its pint-sized target audience. In a word: boogers.

Zachary Gordon once more plays wimpy kid Greg Heffley in 'Diary of a Wimpy Kid: Dog Days,' the third film in the franchise inspired by the Jeff Kinney book series.

More to the point, author Jeff Kinney -- who wrote the popular books on which the "Wimpy Kid" film series is based -- knows just how to tickle the pre-adolescent funnybones of America's McNugget-eaters, and he knows how to do it without crossing any of the lines that would make their parents nervous.

Queasy? Perhaps. But not nervous.

So, yes, in this, the franchise's third installment, there is nose-picking. There is the flabby, hairy horror of public shower rooms. There is pee in the pool. But there's nothing for parents to really, truly worry about in what, like its big-screen predecessors, ends up being an entirely harmless and congenial tale of pre-teen social mayhem.

What's more, there's nothing to keep those same parents from laughing along as its titular wimpy kid -- the average but amiable Greg Heffley -- reminds them of how embarrassing their own parents were back when they first started sprouting armpit hair.

That's not to say "Diary of a Wimpy Kid: Dog Days" breaks any new filmmaking ground. Director David Bowers' story is straightforwardly -- almost unimaginatively -- approached. But, armed with a talented cast and Kinney's chuckle-generating source material, it functions nicely as a sort of big-screen "Wonder Years" for Millennials.

Like 2010's first "Diary of a Wimpy Kid" flick and last year's "Diary of a Wimpy Kid: Rodrick Rules," it also is vaguely reminiscent of certain live-action Disney movies of the 1970s. You know, the ones that starred Kurt Russell and that you enjoyed so much -- but that you remember being much better than they actually are? That's right: these "Wimpy Kid" movies could very well be to your kids what "The Computer Wore Tennis Shoes" was to you.

That is, it's a lighthearted, lightweight romp that knows how to have fun.

There's even a half-hearted message embedded therein, as well. There always is; that's how kids' movies work nowadays. But Bowers -- who also helmed "Rodrick Rules" -- doesn't let anything as pesky as meaning or depth interfere with the silliness.

This time out, he draws inspiration from two of Kinney's books -- "Dog Days" and "The Last Straw" -- as he pits wimpy kid Greg against a classic middle-school enemy: a long, boring summer. The thing is, Greg wants to keep it boring -- and unstructured. His uptight father, meanwhile, would prefer that he do something (gasp!) constructive.

That leaves Greg, with puppy-dog pal Rowley flying wingman, to dream up schemes that will help him enjoy his seventh-grade summer -- that is, schemes that will get Greg within elbow-rubbing distance of the dreamy Holly Hills (Peyton List) -- while keeping dear old Dad at arm's length.

The problem is, trouble and/or public humiliation always seems to find Greg, no matter how well-thought-out he thinks his schemes are.

Most of the cast from the first two films return for this outing, and, by now, they all know their characters well enough to keep things humming. The rotund Robert Capron ("The Three Stooges") is the sweet, but clueless, Rowley. Steve Zahn ("Treme") -- indulging in another amusing fit of comic pique -- is Greg's father. Devon Bostick ("Saw VI") is Greg's big brother, bent on torment.

Then there's Zachary Gordon, as the hapless Greg.

Gordon is making the same career mistake that "Wonder Years" star Fred Savage did in that late, great coming-of-age TV series: He is growing up. But, deeper voice and all, Gordon still plays a convincing everykid. In fact, his easy likability and general relatability are perhaps two of the biggest keys to "Diary of a Wimpy Kid: Dog Days."

Well, that and boogers.

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DIARY OF A WIMPY KID: DOG DAYS3 stars, out of 5

Snapshot: The third family-friendly comedy based on author Jeff Kinney's popular young-reader series sees everykid Greg Heffley struggling to survive the summer between his seventh- and eighth-grade years.

What works: It's all good, clean fun, the kind that will keep young audiences laughing, and their parents smiling alongside them, without fear of anything too terribly offensive spoiling things.

What doesn't: There's nothing particularly deep about the story or imaginative about director David Bowers' approach.